In release 6 of the WCDMA (Wideband Code Division Multiplex Access) specification, a High Speed Up-link Packet Access (HSUPA (also called Enhanced Uplink)) communication scheme is defined in addition to the downlink High Speed Packet Data Access (HSPDA) scheme in order to match the bit rates provided by the latter, so as to cater for improved interactive, background and streaming services. In prior art document 3GPP TS 25.309 “FDD Enhanced Uplink Overall description”, the Enhanced UL is described.
In FIG. 1, a HSUPA network overview (HSDPA related channels are not included in the picture) is indicated. The network comprises a Core Network communicating with a Radio Network Controller (RNC) over the lu interface; a first base station, Node B (B1), a second base station, Node B (B2), both base stations comprising an EUL scheduler unit. The EUL Scheduler is also denoted the MAC-e Scheduler, and communicating with the RNC over respective lub interfaces.
The following HSUPA channels are transmitted over the air interface; the E-AGCH to convey absolute grant signaling from the MAC-e scheduler towards the UEs, the E-RGCH for relative grant signaling, E-HICH to convey acknowledgement feedback from Node-B decoding of UE transmitted data, Dedicated Physical Channel (DPCH) or Fractional DPCH to convey Transmit Power Control (TPC) commands, Enhanced DPDCH (E-DPDCH) to convey the MAC-e payload and Enhanced DPCCH (E-DPCCH) to convey the control signaling of the MAC-e.
Node B1 constitutes the serving cell in this example (E-AGCH is only transmitted from the serving cell), while node B2 constitutes a non-serving cell.
According to the HSUPA specification, the Enhanced Dedicated Channel (E-DCH) high speed uplink transport channel offers a number of new features such as: short Transmission Time Interval (TTI), Fast Hybrid Automatic Repeat Request (ARQ) with soft recombining, fast scheduling for reduced delays, increased data rates and increased capacity.
When a UE is setting up communication with a Node B, 3G paging signals, etc, the setup procedure may be followed by a HSDPA session, for e.g. downloading/surfing an internet page using TCP. Depending on the capabilities of the user entity, this may moreover involve HSUPA transmissions whereby Node B, transmits TCP messages on the E-DPDCH downlink channel which is part of the HSUPA standard and speedy TCP replies are being transmitted on the up-link to Node B. It has been shown that the speed with which the UE can respond over the uplink to Node B, via the TCP protocol, has an impact on the overall downloading speed of larger files from Node B.
After the user entity has been made ready to use a HSUPA service with Node B, the user entity is informed about which E-AGCH code it is supposed to receive absolute grants.
E-AGCH channels are configured to a Node B in a configuration or re-configuration procedure with the RNC via the NBAP signaling protocol. The NPAB E-AGCH channel allocation for a serving radio link (RL) is shown in FIG. 16. Subsequently, downlink traffic is scheduled to UE's on the E-AGCH channelization code in a time multiplexed manner.
One type of message transmitted on the downlink E-AGCH channel are “absolute grants”, that is, messages which grant the user entity, the right to transmit at given bit rates on the up-link. The Node B MAC-e Scheduler issues the absolute grants. Since, bandwidth needs vary dynamically over time; it is beneficial that the power emissions by user entities are regulated speedily, so that bandwidth is not unnecessarily wasted.
The E-AGCH can be defined to have a number of one to several channelization codes (presently, up to four (4)), which number is typically less than the number of E-DCH radio links (RL's) in the cell. The actual number of E-AGCH codes available varies dynamically (but on a rather long time base) over time, the allocation being settled according to procedures between Node B and the RNC. This procedure is shown in FIG. 17.
Since the (number of) E-AGCH channelization codes are limited and since the cell capacity is code and power limited, it is preferred to use as few codes as possible for the E-AGCH transmission. For a MAC-e Scheduler that is changing grants for the UE's frequently, it is important to use the E-AGCH channel efficiently.
Two modes of operation, a 10 ms TTI (Transmission Time Interval) mode and a 2 ms TTI mode are specified by 3GPP. All UE Categories support 10 ms TTI. Category 2, 4 and 6 has 2 ms TTI as an option. Maximum peak rate is 2 Mbps in 10 ms HSUPA TTI and 5.76 Mbps with 2 ms HSUPA TTI. When 4 codes are transmitted in parallel, two codes shall be transmitted with SF2 and two with SF4.
TABLE 1UE Categories in HSUPA, 3GPP TS 25.306MaximumMaximumnumber ofnumber ofbitsbitsMaximumtransmittedtransmittednumber ofwithinwithinHSUPAMinimumSupporta 10 msa 2 msHSUPAcodesspreadingfor 10 and 2 msHSUPAHSUPAMaximumcategorytransmittedfactorHSUPA TTITTITTIBit rateCategory 11SF410 ms TTI only7296—0.73 MbpsCategory 22SF410 ms and 2 ms TTI1459229191.46 MbpsCategory 32SF410 ms TTI only14592—1.46 MbpsCategory 42SF210 ms and 2 ms TTI2000058372.92 MbpsCategory 52SF210 ms TTI only20000—2.00 MbpsCategory 64SF210 ms and 2 ms TTI2000011520 5.76 Mbps
It is likely that only UE Categories capable of handling exclusively of 10 ms TTI will be initially available at the marketplace. Dependent on market success and market demands, it is to be expected that 2 ms capable devices will become available at a later stage.
FIG. 2, corresponding to 3GPP TS 25.211, shows that the transmissions on the E-AGCH for 10 ms TTI's and 2 ms TTI sub-frames are required to be aligned. For both TTI types, the delay is set to 5120 chips in relation to the P-CCPCH channel.
In a prior art scenario, as demonstrated in FIG. 3, where there is a mixture of UE's in a given cell and where some UE's are capable of handling at least 2 ms TTI (in the following referred to as second interval TTI type UE's) and some exclusively 10 ms TTI (first interval TTI type UE's), Node B arranges one or more 2 ms TTI UE's and one or more 10 ms TTI on the same E-AGCH channelization code, i.e. radio link (RL). In the FIG. 3 example, there is a 8 ms transmission gap in case the MAC-e scheduler decides to first transmit an absolute grant to the 2 ms TTI UE and thereafter to the 10 ms TTI UE. “Transmission gaps” on the E-AGCH are likely to arise since the timing properties should fulfill the basic requirement to the starting time as illustrated in FIG. 2. This E-AGCH usage is inefficient and unnecessary extra delays are likely to occur.
It is noted that in the above scenario, the 10 ms TTI are allowed to start on points in time which is an integer number of 10 ms TTI intervals from the given reference time shown in FIG. 2. In-between, the 10 ms TTI transmissions, a number of 2 ms TTI transmissions can take place.